1. Field of the invention
The present invention relates to a lens barrel of a camera having information means capable of generating aperture value information.
2. Description of the Prior Art
With the lens barrel of a camera, a full aperture value and a minimum aperture value are inherently set and intermediate aperture values are available for selection. Such aperture values, or F-numbers, generally are arranged in a specific order for selection as, for example, F2, 2.8, 4, 5.6 and so on, with intermediate values thereof.
The above aperture values are variable with image magnification even when an aperture diameter is fixed. Therefore, even if the aperture value is set to F4 (hereinafter referred to as nominal F-number Fo) for example, an actual aperture value (hereinafter referred to as effective F-number Fe) changes as Fe=Fo *(1+.beta.) when image magnification .beta. is changed by a change in camera-to-subject distance. Generally, an ordinary lens barrel has image magnifications .beta. not exceeding 1/10, in which case the effective F-number is variable within a small range. However, a lens barrel for closeup photography which is sometimes called macro or micro lens has image magnifications of about 1/2 to 1/1, in which case the effective F-number is variable to a great extent to deviate significantly from the nominal F-number. Although proper exposure is achieved if an amount of exposure is determined by TTL metering, improper exposure will result from an exposure control based on the nominal F-number when using a peripheral or external exposure meter or an electronic flash unit of the external metering type. For the latter case, therefore, it is desirable to employ the effective F-number.
On the other hand, the effective F-number assumes various numerical values since it is variable in a continuous manner according to image magnification. Therefore, it is extremely troublesome to read out such numerical values. For comparing aperture values or for determining an amount of stop down from the full aperture value, indications are given by step numbers according to the arranged order mentioned hereinabove. It is, however, extremely difficult to provide such indications when the effective F-number or aperture value is used.
In the case of nominal F-numbers it is easy to provide indications by step numbers since they are arranged in the above-mentioned order. Furthermore, the nominal F-numbers used are restricted to certain specific numbers and have been in common use, wherefore the nominal F-numbers are easy for the photographer to understand.
Additionally, it is sufficient to use the nominal F-number, even when the macro or micro lens is used for taking a normal photography.
Thus, the nominal F-number and effective F-number have their own merits and demerits, and either one cannot meet all of the photographing conditions. This has been very inconvenient to the photographer.